Method and circuit for the operation of electric motors fed by a single-phase supply



p 17, 1940. F. KOVESSI 2,215,156

METHOD AND CIRCUIT FOR THE OPERATION OF ELECTRIC MOTORS FED BY ASINGLE-PHASE SUPPLY Filed July 25, 1936 5 Sheets-Sheet J.

/nventor.-

Wu ATTORNEYS Sept. 17, 1940. KOVESS] 2,215,156

METHOD AND CIRCUIT FOR THE OPERATION OF ELECTRIC MOTORS FED BY ASINGLE-PHASE SUPPLY Filed July 25, 1936 .5 Sheets-Sheet 2 k I a FRANZKovEss: /n vanzor:

i, ATTORNEYS Sept. 17, 1940. KQVESSI 2,215,156 METHOD AND CIRCUIT FORTHE OPERATION OF ELECTRIC MOTORS FED BY A SINGLE-PHASE SUPPLY Filed July25, 1936 5 Sheets-Sheet 5 FRANZ YKOVESSI Inventor:

ATTORNEYS Sept. 17, 1940. KQVESS] 2,215,156

METHOD AND CIRCUIT FOR THE OPERATION OF ELECTRIC MOTORS FED BY ASINGLE-PHASE SUPPLY E Filed July 25, 1956 5 Sheets-Sheet 4 7- Y FRANZKOVESSI lnvemor:

Sept. 17, 1940. KOVESS] 2,215,156

METHOD AND CIRCUIT FOR THE OPERATION OF ELECTRIC MOTORS FED BY ASINGLE-PHASE SUPPLY Filed July 25, 1936 5 Sheets-Sheet 5 L L 5 A 2-FRA/-IZ KOVESSI r7 ver'zt'or:

ATTORNEYS Patented Sept. 17, 1940 UNITED STATES PATENT OFFICE FranzKiivessi, Budapest, Hungary Application July 25, 1936, Serial No. 92,674In Germany July 27, 1935 14 Claims,

My invention relates to a method and circuit for the operation ofelectric locomotives fed by a single phase supply.

Locomotives fed by a single-phase supply and fitted with three-phasemotors are already known, in which the feeding of the motors takes placethrough rotary converters. These systems, however, have the drawback ofa relatively great weight of the machine required therefor and amoderate degree of efficiency, and are partially attended by a low powerfactor.

The invention has for its object the feeding of the multi-phaseinduction motors of locomotives fed with single-phase current throughcontrolled self-guided valves in such a manner that a rotary field isautomatically generated in the motors. The transformation thus takesplace with static apparatuses which are lighter and have a better degreeof efficiency than rotating converters, while the power factor is alsofavourable owing to the manner of operation of the controlled valves.The arrangement also immediately renders possible the connection oftrack motors for three-phase current of 16% periods 5 to the netcarrying single-phase current of 50 periods, whereby the advantage issecured that three-phase current motors may be used with a favourableratio of the number of poles and the air gap. Finally, a furtheradvantage of feeding the motors through controlled valves resides inthat the disconnection of the load may simply take place by blocking ofthe valves, so that the heavy load switches on the locomotive may bedispensed with. It is known already to convert single-phase current intothree-phase current for other purposes by controlled valves but theknown methods had the disadvantage that the valves were only fit forworking upon a net in which threephase current was already flowing,since they were guided by the net, i. e. the arcs once formed in thevalves could only be extinguished by the tension of the net itself.Later the valves have been rendered self-guiding by using special meansfor this purpose, however the present invention differs from'these knownsystems by the fact, that here not only the phase but also the frequencyis converted, and that thereby and by means of a suitable control systemthe valves 50 have been rendered self-guiding without using any furtherauxiliary devices for this purpose. In the accompanying drawings, anumber of advantageous circuits for carrying the invention into effectare illustrated by way of example. 55 Fig. 1 is a diagrammatical View ofone form of the invention showing a motor connected to two rectifiers.

Fig. 2 is a table illustrating the order of energizing the coils in Fig.1.

Fig. 3 is a diagrammatical view of the switch- 5 ing system foroperating the device of Fig. 1.

Fig. 4 is an oscillogram illustrating the current and potential fed tothe motor from the rectifiers.

Figs. 5, 6, 7, 8, and 9 are views similar to Fig. 10 1 showing modifiedforms of the invention.

Fig. 10 is a view similar to Fig. 1 but illustrating the use of arccurrent converters instead of rectifiers.

Fig. 11 is a view similar to Fig. 2 but relating 16 to Fig. 10.

Fig. 12 is a diagrammatical view of the rotating spark gap controllingthe device of Fig. 10.

Figs. 13, 14, and 15 are similar to Figs. 10, ll, 20 and 12,respectively, but relating to a modified form of the invention utilizingthree are current converters.

Figure 1 shows a three-phase current motor M fed through two six-polegrid-controlled recti- 25 fiers Gli and Glz. The anodes Al-fi and Ai' s'of the two rectifiers are connected in parallel and connected with theends l6 of the coils Sim-a of the stator winding of the motor, while thecathodes k1 and R2 of the rectifier-s are con- 30 nected to the ends ofthe secondary Winding of the supply transformer T. The coils Sp1 x ofthe motor are tapped in the centre and the tapping points are connectedtogether and to the zero point 0 of the supply transformer. 5

Owing to the valve action of the rectifiers, the current induced in thesecondary Winding of the supply transformer can only flow in thedirection cathode to coil centre. The rectifiers thus always operatealternately with the halves of the transformer associated with them andthe current supply to the motor takes place constantly from the zeropoint of the transformer to the coil centres.

As the condition necessary for the parallel 45 operation of the anodesof the rectifiers, namely equal potential with respect to the cathode,is fulfilled, the current could flow all at once through all six coilhalves of the motor. Now, in order to generate a rotary field in themotor, that is, to dephase the currents flowing through the individualcoil halves in point of space and in point of time with respect to oneanother, the control grids 9H; and g1-s are used.

The manner of operation of the grids necessary for this purpose will beseen from Figure 2. The six vertical columns in the table represent sixconsecutive periods of time, the duration of one period of timecorresponding to a half-wave of the supply current. Within this time,the direction of the current remains the same in all parts of thecircuit.

In the first horizontal line of the table the dot-and-dash vectorsindicate that direction of the field in each period of time which isnecessary in order that a rotary field may be produced. The fullydrawn-out vectors show how the components must act in the direction ofthe coil axes I, II and III in order to afford the desired result.

From the vector diagrams of the first line the figures of the secondline are obtained. The three coil axes I, II and III are here identifiedby horizontal lines, the centre vertical line representing the coilcentres, that is, the point of the current feed. From here, the currentin the various coils may flow to the right or to the left, according towhich of the anodes connected to the coil ends are ignited. Thedesignations l5 here used for the coil ends are the same as in Figure 1,that is, the outer coil parts are shown to the left of the centre lineand the inner coil parts to the right thereof.

Assuming that the coils are so wound that the direction in which thecurrent fiows through corresponds to the direction of the generatedfield, the field directions drawn in line I can immediately be comparedwith the current directions illustrated in Figure 2. For example, in thefirst column the field in the coil axis I is directed outwards, so thatthe current in line 2 must also flow outwards, i. e. from the centre ofthe coil to the left to the coil end Consequently, in this period oftime the anodes a1, ai, must be ignited, but not the anode a4, a4. Inthe same way, it follows that of the remaining anodes in the same periodof time, the anodes (15, W5 and as, lZs must be ignited, while in thefollowing period of time the anodes a1, a'1, a2, az, do, as must beignited, and so on.

The order of succession of the ignition of the anodes which is necessaryfor the generation of a rotary field having thus been established, thecontrol device for controlling the grids may readily be produced withthe aid of the third line of Figure 2, in which a field is allocated toeach of the pairs of grids g1 s, g1 s, the hatched fields in each columnshowing the pairs of grids to be connected simultaneously to thepositive terminal oi the ignition current source. The remaining gridsare connected to negative potentials and the anodes associated therewithare consequently blocked.

Figure 3 shows the control device St. for the grids in diagrammaticform. The contact roller W is driven by a small synchronous motor havingsix poles and connected to the supply, which is shown in the drawings,and its speed consequently amounts to one third of the synchronous speedcorresponding to the supply frequency. The surface of the roller is halfconductive, its other half being covered with insulating material. Theconductive coating is connected through a slip ring s to the positivepole of the battery B, while six brushes b1 s distributed uniformly overthe circumference of the roller are connected in the order of successionshown in line 3 of the table in Figure 2 through resistances w with thegrids g1 e of the rectifier and through resistances r with the negativepole of the battery. The centre point of the battery lies at the cathodeis of the rectifier. As the cathodes of the two rectifiers always havedifferent potentials, a separate control device must be provided foreach rectifier, but the rollers thereof must be mounted onthe same shaftfor the purpose of exact synchronism, namely in such a manner that theposition of the conductive coatings with respect to the brushes isexactly equal in both.-

The ignition must take place when the potential has the value zero, thatis to say, the control device must operate the grids at the end of eachhalf-wave of the supply current. In this way, the resulting vector ofthe field is turned forward through 60% after each half-wave. Theturning of the field takes place intermittently, and consequently aseries of upper fields arises in addition to the basic field. The basicfield turns at a constant speed, which corresponds to one third of thesynchronous speed of the supply; with a. supply frequency of 50 periods,the motor is thus a three-phase motor operating with 16 periods.

The ripple potential fed to the motor generates in the motor a ripplecurrent, as shown in the oscillogram in Figure 4, in which the curve 0represents the current of 16 periods, 1) the potential of 50 periods andc the potential of 16% periods. The power factor of the current takenfrom the mains thus becomes favourable in view of the smallness oftheripple. As will be seen from the oscillogram, the power taken up by themotor is, owing to the ripple, in equilibrium with the power yielded bythe supply, so that a special energy accumulator is not necessary.

In order to prevent a great direct current component from being set upin the motor and thus to keep the motor currents in equilibrium, it isadvisable to effect the current feed to the coils in the mannerillustrated in Figure 5 through a suction choke D which is interposed atthe tapping points of the coils between the two coil halves.

Figure 6 shows another form of the circuit, in which instead of twosix-pole rectifiers a sixpole and a two-pole rectifier are used. Thetappings of the coils Spi-a are here connected with the cathode In ofthe two-pole rectifier G11, the anodes a1 and oz of which lie at theends of the secondary winding of the supply transformer T. The zeropoint of the supply transformer is connected with the cathode k2 of thesix-pole rectifier G22, the anodes (1'1-6 of which are connected to theends l-6 of the coils of the motor.

Figure '7 shows a further form of the circuit with a single six-polerectifier G1 with two cathodes k1 and la the anodes a1 a of which areeach provided with two control grids gi-e, gi-a. The control of the twosets of grids is effected by two separate control devices according toFigure 3. The tappings of the coils S1914 are here directly connectedwith the zero point of the supply transformer T, the two ends of whichare connected to the cathode of the rectifier. The anodes (11-6 of therectifier are here also con-' nected with the ends I-B of the coils ofthe motor.

According to Figure 8, a twelve-pole rectifier G1 is used and the motoris provided with double coils 5101-3, Sp'1 3. The tappings of each setof coils are connected with the ends of the secondary winding of thesupply transformer T, the zero point of which lies at the cathode k ofthe rectifier. The anodes (11-12 of the rectifier are connected with theends l-|2 of the coils of the two sets of coils.

In the form according to Figure 9, the supply transformer is omitted;the two poles of the supply are connected direct with the cathodes K1.K: of the two rectifiers Gli, GI: and with the tappings of the two setsof coils. The anodes ai-e, a'i-a again lie at the ends l-l2 of the twosets of coils.

In cases where two rectifiers are used, it is also possible to travelconstantly or periodically only with one of the rectifiers, in whichcase only one half-wave oi the supply current is used. This affords theadvantage that the operation may be continued even in the event ofdisturbance of one of the ,rectifiers.

Of course, instead of the rectifiers so far shown, other types of valvesmay be used, in particular the arc current converter, especially as thecompressed air necessary for this purpose is in any case available onthe locomotive. Fi ure shows the circuit when using six such valves L1s. The tapping points of the coils S n-3 are here connected direct withone pole of the supply, while the ends l-6 of the coils are connectedthrough the arc current converter Ll-6 with the supply.

Figure 11 shows the table, formulated in a corresponding manner to thetable in Figure 2, for effecting the control of the valves. In the firstline, the current directions necessary for generating the rotaryfield inthe three coils I, II, III of the motor are represented, the second lineindicating the momentary current direction in the supply. In the thirdline the coil halves to be provided in each period of time with currentare indicated by hatching and in the fourth line the arc currentconverting vessels to be ignited in each case are shown. Figure 12 showsthe corresponding formation of the rotating spark gap serving to controlthe arc current converters.

In Figure 13 another form of the circuit with only three arc currentconverters L1 a is shown, in which the tappings of the coils Sin-a ofthe motor are again directly connected with one pole of the supply,while the end of each coil is connected together with the beginning ofthe next coil through an arc current converter with the other pole ofthe supply. Figure 14 shows the table, formulated in accordance withFigure 11, for determining the control of the current converters andFigure 15 shows the necessary construction of the rotating spark gapserving for the control.

The circuit according to the invention is not only suitable foroperation with synchronous speed of the control device, but also withany smaller speed, the induction motor always having as synchronousspeed the speed of the control device. The possibility is thus affordedof making the induction motor run asynchronously; to this end, only thecontrol device needs to be provided with a small automatically startingsingle-phase commutator motor in addition to the synchronous motorserving for the normal drive. Upon starting of the small motor, the

" large motor also starts; however, the synchronous operation isconnected with increased losses and it is therefore advisable to connectthe synchronous motor connected with the control device with the mainsimmediately the synchronous speed is reached.

The use of an automatically starting motor for driving the controldevice has the further advantage that in this the induction motor may beprovided with a short-circuited rotor, whereby in addition to the greatsimplification of the motor itself the starting resistance may also bedispensed with; furthermore, it is thus possible also to increase theoperating potential and consequently to bring about a furtherimprovement of the degree of efficiency. The induction motor naturallyalso renders possible a regenerative braking of the vehicle. Instead ofthe threephase motor shown in the constructional examples, a motorhaving any other phase number may naturally also be used.

Having now particularly described and ascertained the nature of myinvention and in what manner the same is to be performed, I declare thatwhat I claim is:

1. In a circuit for a multiphase induction motor, said motor'having nphases, a plurality of poles and a plurality of stator coils, means forsupplying a single-phase current to said circuit,

control valves comprising at least one cathode,

a plurality of anodes, and control grids for said anodes, said controlvalves being connected to said supply means and being connected inseries to said stator coils; control means for said grids comprising arotary distributor connected to said grids, and a synchronous motorconnected to said single-phase supply current for driving saiddistributor, said motor having a number of poles equal to at least twicethe number of phases of said multiphase motor.

'2. In a circuit for a multiphase induction motor, said motor having 12phases, a plurality of poles and a plurality of stator coils, means forsupplying a single-phase current to said circuit, control valvescomprising at least one cathode, a plurality of anodes, and controlgrids for said anodes, said control valves being connected to saidsupply means and being connected in series to said stator coils; andmeans for connecting said supply means to the centers of said coils,control means including a rotary distributor connected to said controlgrids, and a synchronous motor connected to said single-phase supplycurrent for driving said distributor, said motor having a number ofpoles equal to at least twice the number of phases of said multiphasemotor.

3. In a circuit as in claim 2, a suction choke interposed in said meansconnecting said supply means and the centers of said coils, the currentsupply side of said supply means being connected to the center of saidchoke.

4. In a circuit as in claim I, a second selfstarting motor connected tosaid distributor.

5. In a circuit as in claim 1, said multiphase motor having ashort-circuited rotor, and a second self-starting motor connected tosaid distributor.

6. In a circuit as in claim 1, a second selfstarting single-phasecommutator motor connected to said single-phase supply current and tosaid distributor.

7. In a circuit as in claim 1, said control valves consisting of groupsof anodes and corresponding groups of control grids, a cathode comemonto each of said groups, and said control means comprising a rotarydistributor for each of said groups.

8. In a circuit for a multiphase induction motor, said motor having 12phases, a plurality of poles and a plurality of stator coils, means forsupplying a single-phase current to said circuit, means for connectingsaid supply means to the centers of said coils, control valvescomprising at least one cathode and a plurality of anodes, and controlgrids for said anodes, means for connecting said valves to the ends ofsaid coils, control means including a rotary distributor connected tosaid control grids, and a synchronous motor connected to saidsingle-phase supply current and to said distributor for driving saiddistributor, said motor having a number of poles equal to at least twicethe number of phases of said multiphase motor.

9. In a circuit as in claim 8, said ends of said stator coils beingconnected to said valves through said anodes, and said cathode beingconnected to said current supply means.

10. In a circuit as in claim 8, said coils being composed of at leasttwo parts, each of said parts being connected by said connecting meansto said supply means by center taps, the ends of each of said partsbeing connected by said valve connecting means to said valve throughsaid anodes, said cathode being connected to said current supply means.

11. In a circuit for a three-phase induction motor, said motor having aplurality of stator coils and a plurality of poles, means for supplyinga single-phase current to said circuit, means for connecting said supplymeans to the centers of said coils, control valves comprising at leastone cathode and a plurality of anodes and control grids for said anodes,means for connecting said valves to the ends of said coils, and controlmeans including a rotary distributor connected to said control grids,and a synchronous motor having six poles and connected to saidsingle-phase supply current ior driving said distributor.

12. In a circuit for a multiphase induction motor, said motor having nphases and a plurality of stator coils, means for supplying asingle-phase current to said circuit, a transformer having primary andsecondary windings, said primary winding being connected to said supplymeans, a control valve connected to said secondary windings, saidcontrol valve being composed of two cathodes, a plurality of anodes, andcontrol grids between said anodes and cathodes, said cathodes beingconnected to the ends of said secondary windings, means connecting thecenter of said secondary winding with the centers of said coils,

means connecting each end of said coils to an anode, and control meansfor said grids comprising a rotary distributor connected to said controlgrids, and a synchronous motor connected to said single-phase supplycurrent for driving said distributor, said motor having a number ofpoles equal to at least twice the number of phases 0! said multiphasemotor.

13. In a circuit for a multiphase induction motor, said motor having nphases and a plurality of stator coils, each of said coils consisting ofat least two parts, means for supplying a singlephase current to saidcircuit, at least two control valves, each of said control valvescomprising a cathode, a plurality of anodes, and a control grid for eachanode, means for connecting said supply means to the cathode of eachvalve and to the center tap of each of said coil parts, means forconnecting the ends of one part of each coil to an anode in one of saidvalves, means for connecting the ends of another part of each coil to ananode of another of said valves, and control means for said gridscomprising a rotary distributor connected to said control grids, and asynchronous motor connected to said singlephase supply current fordriving said distributor, said motor having a number of poles equal toat least twice the number of phases of said multiphase motor.

14. In a circuit for a multiphase induction motor, said motor having nphases and a plurality of stator coils, means for supplying asingle-phase current to said circuit, a control valve system comprisinga plurality of compressed air operated arc converters, means connectingsaid control valve system to said supply means and to the ends of saidcoils, means for connecting said supply means to the centers of saidcoils, and control means for said valve system comprising a rotary sparkgap device connected to said are current converters, and a synchronousmotor connected to said single-phase supply current for driving saidrotary spark gap device, said motor having a number of poles equal to atleast twice the number of phases of said multi-phase motor.

FRANZ KOVESSI.

